1. Field of the Invention
This invention relates to a solid state color television camera having a solid state image sensing device wherein an image signal processing is executed for generating a composite color video signal.
2. Description of the Prior Art
It has been customary in a color video camera to achieve a white balance control in order not to cause changes in a white part of an image due to the temperature of a light source. Also, in a single plate television camera, wherein the single solid state imager performs a color image sensing, a complementary color filter with a high light utilization efficiency is provided to an image sensing optical system as a color separating filter to perform a color iamge sensing by a field-accumulated image sensing device so as to improve an image sensing sensitivity or a dynamic resolution, etc.
In such type of a color television camera, an imaging operation is performed using an image sensing element with a complementary color filter for color coding provided on its image sensing plane in which color filters of magenta (Mg), green (G), cyan (Cy), yellow (Ye), for example, are arranged in a mosaic pattern as seen in FIG. 2. Thus there is obtained an image sensing output which is an additive synthesis of signal electric charges of L.sub.(N) line and L.sub.(N+1) line as an image sensing output of an odd field. Similarly, an image sensing output which is an additive synthesis of signal electric charges of L.sub.(N+1) line and L.sub.(N+2) line is obtained as an image sensing output of an even field. From the aforementioned image sensing element with the complementary color filter, an image output (S.sub.o) wherein (Mg+Cy) output and (G+Ye) output are repeatedly produced and an image output (S.sub.E) wherein (Mg+Ye) output and (G+Cy) output are repeatedly produced are line sequentially produced.
As shown in FIG. 3, in the conventional devices, a color video signal was formed by supplying the image sensing output obtained by the above-described image output element to an image sensing signal processing circuit.
In FIG. 3, the numeral 20 indicates the image sensing element with said complementary color filter, 21 indicates a first low-pass filter (LPF.sub.H) that picks up a wide band luminance signal Y (Y.sub.H) from the image sensing output (S.sub.O)/(S.sub.E) obtained as a line sequential output by the image sensing element 20, 22 indicates a second low-pass filter (LPF.sub.L) that picks up a narrow band luminance signal (Y.sub.L ') from the image sensing output, and 23 indicates a band-pass filter (BPF) that picks up a chroma signal (C) from the image sensing output.
The first low-pass filter 21 forms a wide band luminance signal Y (Y.sub.H) by excluding a space sampling carrier component produced by the complementary color filter from the image sensing output (S.sub.O)/(S.sub.E). The wide band luminance signal Y (Y.sub.H) is supplied to a color encoder 39.
Also, the second low pass filter 22, the cut-off frequency of which is lower than that of the first low-pass filter 21, forms a narrow band luminance signal (Y.sub.L ') by excluding a space sampling carrier component. This narrow band luminance signal (Y.sub.L ') is supplied to a signal adder 27, 28 as a white balance control signal (.+-..DELTA.Y) via a variable gain amplifier 24, 25.
Further, in the band-pass filter 23, the space sampling carrier component produced by the complementary color filter, i.e. a chroma signal, is picked up from the image sensing output (S.sub.O)/(S.sub.E) to be supplied to a synchronous detection circuit 26.
The synchronous detection circuit 26 performs a synchronous detection of the chroma signal picked up from the image sensing output (S.sub.O)/(S.sub.E) with a carrier signal corresponding to the space sampling carrier component so as to produce an output of a line sequential color difference signal (R-Y')/(B-Y'), hereinafter denoted by (C.sub.1)/(C.sub.2).
Then, there is provided an additive synthesis of the white balance control signal (.+-..DELTA.Y) in the signal adder 27, 28 to the line sequential color difference signal (C.sub.1)/(C.sub.2) that was outgoing from the synchronous detection circuit 26, which is supplied to the simultaneous circuit 31 direct from a signal selecting circuit 29 or via a one horizontal period (1H) delay circuit 30.
The line sequential color difference signal (C.sub.1)/(C.sub.2) to which a white balance control has been already achieved is converted from the line sequential system to the simultaneous system due to the simultaneous circuit 31.
It is to be noted that when the color temperature of the object the image of which is picked up in the image sensing element 20 varies from the normally-set color temperature to the higher one, each color difference signal (C.sub.1)/(C.sub.2) changes the state indicated by a line to the state indicated by a chain-dotted line, both of which are shown in FIGS. 4(A) and 5(A). Also, the luminance signal (Y) changes the state indicated by a line to the state indicated by a chain-dotted line in FIG. 6. Therefore, it is possible to execute a white balance control as shown in FIGS. 4(C) and 5(C), by generating a white balance control signal (.+-..DELTA.Y) indicated by the chain-dotted lines in FIGS. 4(B) and 5(B) from the narrow band luminance signal (Y.sub.L '), and by performing an additive and subtractive synthesis of said white balance control signal (.+-..DELTA.Y) with each color difference signal (C.sub.1)/(C.sub.2) such that the waveformed integral value shown in FIGS. 4(A) and 5(A) becomes zero.
However, even by this white balance control, each color difference signal (C.sub.1)/(C.sub.2) changes its sensitivity due to the wave length, and results to have characteristics different from a spectral sensitivity (response) at the normally-set color temperature.
Hence, in regard to the respective color difference signals (C.sub.1)/(C.sub.2) that were outgoing from the simultaneous circuit 31, it has been customary to perform a compensation beforehand to the changes of the color temperature in a color temperature control circuit 38, and then to generate a color video signal of a standard television system, such as an NTSC system, in a color encoder 39 to let it outgo from a signal output terminal 40. In this connection, the color temperature control circuit 38 is also called as a linear matrix circuit, where there is performed an additive synthesis of the respective color difference signals (C.sub.1)/(C.sub.2) in each signal adder 36, 37 via variable gain amplifiers 32, 33, 34, 35 wherein the gain varies according to the color temperature so as to control the spectral sensitivity characteristics.
As earlier noted, with the known image sensing signal processing circuit wherein the white balance is controlled by providing an additive and subtractive synthesis of the white balance control signal (.+-..DELTA.Y) to each color difference signal (C.sub.1)/(C.sub.2), it becomes impossible to maintain the color reproducibility because of the change in the spectral sensitivity characteristics caused by the change of the color temperature. So it is necessary to provide a color temperature control circuit having complicated circuit structure in order to control the changes of the spectral sensitivity characteristics.